1. Field of the Invention
This invention relates generally to elastomeric fluid control valves and more specifically to valves having a duck bill configuration.
2. Discussion of the Prior Art
Elastomeric valves are commonly used to control the flow of fluids. Valves of particular interest to the present invention are formed from a pair of walls, each having a generally planar configuration, which converge and intersect along a line or slot. With this configuration, these valved are commonly referred to as "duck bill" valves.
The duck bill valves are particularly adapted to enable fluid flow in one direction while inhibiting fluid flow in the opposite direction. These characteristics are particularly appreciated in surgical access devices which control the flow of fluids such as blood (in the case of endoscopes) or gasses (in the case of trocars).
The duck bill valves of the past have not been particularly suited for use as valves in those environments where surgical instruments are to be inserted through the valve. In these cases, valve is required to form a seal with the outer surface of the access device in order to maintain a gas or fluid pressure at the distal end of the device. When an instrument is inserted into a duck bill, it passes between the converging walls of the valve and through the slot at the distal end of the valve. This causes the walls to separate and to create an undesirable flow channel between the slot and the instrument. This phenomena is commonly referred to as the "cat-eye" effect.
In some case valves have been used with endoscopes wherein guidewires have been inserted through the valves. Where a particular procedure demands that the endoscope be removed leaving the guidewire in place, reinsertion of the endoscope over the guidewire has required backloading of the valve. Such backloading is particularly difficult with duck bill valves since the distal end of the valve is configured only with the narrow shape of the slot.
For these reasons the duck bill valves of the past have not been suitable for use in medical access devices particularly when such a device must accommodate insertion and removal of a surgical instrument.